Whenever I run a flashpoint as a tank or healer, before we begin I tell the team (if healer) that if dps pulls a mob I wont heal them they can die or leave I dont care there are to many dps'ers in this game. As a healer my main focus is keeping the tank alive. As a tank I will always protect the healer first and maintain my aggro. Dps are expendable.
If DPS pull aggro (on the main mobs the tank is trying to hold), it's the tank doing something wrong 90% of the time unless both DPS significantly outgear him. Otherwise the super geared DPS should be guarded to fix the problem, or the tank need to get better at his rotation. You should be able to hold it from anyone other than an unguarded powertech (due to lack of threat dump) even if they go all out.